Method of and means for utilizing charged-particle radiation



Aug 29, 1950 E. G. UNDER METHOD 0F AND MEANS FOR UTILIZINGCHARGED-PARTICLE RADIATION Flled Sept 25 1948 INVEITOR Ernes Lmder BYA'L'TORNEY Patented Aug. 29, 1950 METHOD 0F AND MEANS FOR UTILIZING i iCHARGED-PARTICLE RADIATION iii-nentJ G. Linder, Princeton, N. J., 'minorto Radio Corporation ot America, a corporation o! Delaware vApplicationSeptember 25, 1948, Serial No. 51,206

f 1s claims. (ci. 111-330) This invention relates to electron sourcesand beams and more particularly to electron beams and multipliersobtained by secondary electrons emitted upon bombardment by nuclearparticles.

It is known that certain isotopes are radioactive and emit nuclearcharged particles at known rates over known periods of time and over arange of energy values or levels expressed in electron volts. Someemissions consist of positively charged or alpha particles, others ofnegatively charged or beta particles and others of both alpha and betaparticles.

With the emission of a charged particle from the nucleus of an atom,there occurs a transn mutation of the atom into an atom of anotherelement and this atom may or may not be radioactive and it may or maynot be gaseous in form.

It is also known that when certain materials are subjected to nuclearradiation bombardment, electrons around the nuclei of the bombardedatoms are knocked out of their orbits and projected into space. Thisphenomenon is known as secondary emission. The number oi secondaryelectrons emitted per bombarding particle depends in general upon thematerial itself and upon angleof incidence and the velocity of thebombarding particle. In general, the greater the angle of incidence andthe less the velocity of the bombarding particle, the greater is thenumber of secondary emitted electrons.

These secondary emitted electrons usually have relatively low energyvalues compared with the primary emission values. Their furthermovements after leaving the bombarded surface depend upon their initialvelocities and their initial random direction and upon the electro-`trode ofthe tube and 'with sufilcient energy as to i i cause secondaryelectron emission. Also phosphorus2 becomes stable after emission and isparticularly adapted to high vacuum tube use as its decay products arenot gaseous. There are, however, a large number of other suitableradioactive substances that may be used within the scope of theinvention.

The instant invention comprises improvements on the methods and systemsdisclosed and claimed in copending U. S. application Serial No. 49,736illed September 17, 1948, which basic invention contemplates the use ora source of radio-active material and an'electrode that issecondaryemission responsive to the charged particle radiation thereof,the space between the source and the electrode being under partialvacuum and also subjected to a constant magnetic field and the sourceand the bombarded electrode being connected to an external load circuitin which is provided an electric potential source to keep theradio-active source electrode (cathode) positive in respect to thebombarded electrode (anode).

The improvement of the instant invention comprises the addition of anelectrode maintained at a high positive potential near one end of thebombarded anode to draw the electrons from their trapped paths andproject them in the form of a beam or collect them on the thirdelectrode and thus secure electron multiplication. In both cases the owof electrons may be modulated to obtain amplincation of an electricalmodulated source.

Among the objects oi the invention are to provide an improved method ofand means for producing electron beams.

Another object of the invention is to produce sources of electrons andcollect the electrons.

Another object of the invention is to provide an electron multiplier. j

Another object of the invention is to provide an electron beam and tomodulate the beam in accordance with a signal, such as a source ofalternating current or a modulated current.

Another object of the invention is to provide a new method and means forcausing secondary emission of electrons.

Other objects may be apparent from the disclosure of the invention ashereinafter set forth in detail and from the drawing made a partM hereofin which Figure 1 is a schematic diagram of the said basic inventiondisclosed in said copending application; Figure 2 is a schematic diagramof the instant invention including a third electrode, such as one nearthe end of the bombarded electrode; Figure 3 is another schematicdiagram of the invention and is similar to Figure 2 except that there isprovided a modulated voltage to modulate the electron beam; Figure 4 isa schematic diagram of the invention showing a collector electrode nearone end of the bombarded electrode and providing tor modulation for theelectron beam; and Figure is similar to Figure 4 except the providedmodulation ls accomplished by a grid positioned between the source ofthe radioactive material and the bombarded electrode.

Similar reference characters are applied to similar elements throughoutthe drawings.

Referring to Figure 1, which is a schematic diagram of the basicinvention disclosed in said pending application, I is a nuclear energygenerator tube consisting aof a source oi radioactive material 2 mountedon a conducting support l, the source 2 and the support l acting as oneelement of the tube I.

This element of the tube will be referred to throughout the specicationand claims as the source or radioactive source."

The other element of tube I is the collector electrode 4, which may beof one oi various shapes, shown in this case as a cylinder of sheetmaterial. This electrode il is secondary-electron emission responsiveupon bombardment by the charged particles emitted from source 2.Aluminum has been found to be a suitable material for electrode 4. Anexternal load 5 is connected between source 2 and electrode 4 and inthis load circuit is inserted, in series, a source of electricalpotential B, the positive pole ofwhich is connected to source 2, thatthe source 2 is positive in respect to electrode 4. Source 2 andelectrode 4 are surrounded by an envelope 1 [made of some nonmagneticmaterial such as lglass and is adapted to exhaustion to a residualpressure of the order of -3 mm. of Hg or loweriby any conventionalmeans, not shown. 'I'he residual gaseous medium secondary emissionelectrons from electrode 4, f'

and the electrons produced by gaseous ionization, but principally fromthe latter.

Referring to Figure 2, there are provided a source of radioactivematerial 2, an electrode 4 in the form of a cylinder of sheet material,a solenoid 8 and a source of direct current 9. There is also provided anelectrode I0, which is also shown in the form of a cylinder of sheetmaterial. This electrode Ill will be referred throughout thisspecication and the claims as the accelerating electrode. oraccelerator. Accelerator I0 is connected to electrode 4 through a highpotential electrical source I4. The electrode 4 is connected to thenegative pole of electrical source 6, the positive pole of which isconnected to source 2, that the source 2 may be biased and maintainedpositive in respect to electrode 4. Electrode 4 may be grounded as atI2. 'I'he theory upon which the observed amplification of electrons isaccomplished by the arrangements disclosed in Figure l, is not fullyknown but it is believed to be that when the electrode 4 is bombarded'byparticles from source 2, and in the absence of a magnetic eldtherebetween, a current will flow through the external load, connected,for example, to any suitable collector electrode, not shown, which isresponsive to the impingement of the beam Il thereon, as shown in Figs.4 and 5. Some secondary electrons from electrode 4 will travel to source2 but, in general, the current through load 5 will be approximatelyequal to the primary emission current of source 2. When, however, aconstant magnetic ileld is impressed in the space between and parallelto the source 2 and the electrode 4, primary and secondary electrons aredeected in their paths, the primary electrons striking electrode 4 atoblique 4 angles and thus causing a greaterl secondary -cuit may begrounded as at I2.

emission of electrons than when striking normal to electrode 4 and thesecondary electrons being reilected successively by electrode 4, ortrapped within the space, until under certain conditions of the magneticileld and the pressure of the medium, the paths of the electrons exceedthe mean free path for ionization by collision with molecules of themedium and ionization of the medium occurs, making the mediumconductive. This results in an enormous increase in current from thecopious supply of electrons made available mainly by gas ionization.

Applying this theory to the instant invention, as disclosed in Figure 2,the copious supply of electrons within thespace between the source 2 andelectrode 4 are subjected to two forces: (1) the magnetic ileld createdby the solenoid 8 which causes the electrons emitted by secondaryemission upon bombardment of electrode 4 by the primary electrons ofsource 2, as well as the electrons emitted upon bombardment of electrode4 by the secondary emitted electrons, and also electrons produced by gasionization to follow curved paths as their velocities are spent and (2)the electrostatic field created by the electric source I 4 which sets upa difference of potential between accelerator I0 and electrode 4 and adifference of potential between accelerator I0 and source 2. Theelectrons are therefore drawn from the space between source 2 andkelectrode 4 and are accelerated in the form of an electron beam, I3.

Referring to Figure 3, the arrangement disclosed therein is similar tothat disclosed in Figure 2, except that the magnetic eld is supplied bya permanent magnet I5, on which is disposed the radioactive material 2.Also, in Figure 3, there is included the secondary coil I6 of atransformer, which is connected in series between the biasing electricsource 6 and the magnet I5, The negative pole of electric source 6 isconnected to the negative pole of electric source I4. The cir- Theprimary coil I1 of the transformer is connected to a source of electricypotential, either an alternating or a modulated source, such as signal.

In operation, the permanent magnet l5 creates the magnetic field, havinga component as shown by arrow H, which deflects the paths of, theprimary and secondary electrons to trap them in the space between thesourcel.` and electrode 4, as previously disclosed. 'I'he electrons arealso subject to the electrostatic field created by the electricalpotential I4 andare accelerated as a beam along the axis of acceleratorI0.

It is apparent that a variation of the potential impressed on magnet I5will vary the' flow of electrons along beam i3. When the potential ofsource 2 becomes progressively less positive, electrons are repulsedvmore and more by the lower electrostatic eld around source 2 and moreelectrons are available to be drawn into beam I3. Also when thepotential of source 2 asaaeos the form of a flat electrode. Theseelements are mounted in envelope 1. The magnetic iield,

. created by solenoid 8 connected to direct current source 9, is atright angles to the longitudinal axis oi' electrode I8 and electrode 4,as indicated by H.` The magnetic iield and the electrostatic field,created by electric source I4, react on the primary and secondaryemission electrons and deflect them along the path I9. As the electronsstrike electrode 4, at points `ill, 20, further secondary emissionoccurs. There is thus created a copious supply of electrons and thelengths of their paths are increased beyond the mean free path forionization by collision with molecules of the medium, causing gasionization and the iiow oflarge currents to the collector -plate 2|.Collector 2| is connected to electrode I8 through electric source I4,load 5, the secondary coil I6 oi' a transformer and biasing electricsource 6. The drop of potential along load 5 is available i'or use in anoutside circuit (not shown) or the current passing through load may beused in load 5 to perform a useful function. Electrode 4,is grounded atI2 as well as the lead between `load 5 and coillli.

The flow of electrons between electrode I8 and electrode 4 may bemodulated in the same manner as disclosed in connection with Figure 3.The secondary coil I6 of a transformer, connected to electrode I8, willimpress upon electrode I8 electrostatic potentials in accordance withthe a1- ternations or the modulations of currents ilowing through theprimary coil I'I of the transformer. The potentials on electrode I8 arebiased by electrical source 6 connected between coil I6 and theelectrode I8.

`The disclosure in Figure 5 is similar to that in Figure 4, except thatthe modulation is accomplished by inserting a, grid 22 between thesource 2 and electrode 4. Grid 22 is connected Ito the secondary coil I6of the transformer, the

other end of the coil being connected to the collector 2I through load 5and electric source I4.

The primary coil I'I of the transformer is connected to the source ofthe modulated current or signal. The electrode I8 is connected throughbiasing electric source 6 grounded at I2 and to collector 2I throughload 5 and electric source I4. Electrode 4 is grounded at I2.

It is apparent that grid 22 will affect the disposition of electrons inthe space between electrode I8 and electrode 4, when an alternating ormodmaung potential is napressed upon the grid ondary particles to amagnetic field to deflect said source lparticles against said materialat oblique angles and to deiiect said secondary particles successivelyagainst said material to provide i'urther secondary emission particlesand to extendthe paths of said secondary particles bepositive. theelectro- 6 yond the mean free path for ionization by collision with themolecules ot the medium to provide further particles, and impressing onsaid medium an electrostatic eld to accelerate said particles into abeam.

2. The method of utilizing a source of radioactive charged-particleradiation for creating and collecting an electron beam comprising:exposing to said radiation a secondary-emission charged-particleradiation responsive material in a confined gaseous medium. subjectingsaid source and secondary particles to a magnetic iield to deect saidsource particles against said material at oblique angles and to deiiectsaid secondary particles successively against said material to providefurther secondary emission particles and to extend the paths of saidsecondary particles beyond the mean free path for ionization bycollision with the molecules of the medium to provide further particles,impressing on said medium an electrostatic field to accelerate saidparticles into a beam, and collecting said particles in said beam.

3. The method of utilizing a source of radioactive charged-particleradiation for creating and utilizing an electron beam comprising:exposing to said radiation a secondary-emission electron radiationresponsive material in a coniined gaseous medium, subjecting said sourceparticles and said electrons to a magnetic field to deiiect said sourceparticles against said material at oblique angles and to deflect saidelectrons successively against said material to provide furthersecondary emission electrons and to extend the paths of said electronsbeyond the mean free path for ionization by collision with the moleculesof the medium to provide further electrons, impressing on said medium anelectrostatic field to accelerate said particles into a beam, collectingsaid electrons in said beam, and utilizing the currents produced by theiiow of said electrons.

4. The method of utilizing a source of radioactive charged-particleradiation for creating and controlling an electron beam comprising:exposing to said radiation a secondary-emission electron radiationresponsive material in a coniined gaseous medium, subjecting said sourceparticles and said electrons to a magnetic field to deiiect said sourceparticles against said material at oblique angles and to deiiect saidelectrons successively against said material to provide furthersecondary emission electrons and to extend the paths of said electronsbeyond the mean free path for ionization by collision with the moleculesof the medium to provide further electrons, impressing on said medium anelectrostatic iield to accelerate said particles into a beam, andvarying the electrostatic potential of said source to cause variationsin the density of said electrons in said beam.

5. Apparatus for creating a charged-particle beam including: aradioactive source providing charged-particle emission, means disposedin a region adjacent said source that are secondaryemissioncharged-particle radiation responsive to said source, said source andsaid responsive means y being disposed in a coniined gaseous medium,means for impressing a magnetic eld on said source particles to deflectsaid source particles against said responsive means at oblique anglesand to deflect said secondary particles successively against saidmaterial to provide further secondary emission particles and to extendthe 7 paths of said secondary particles beyond the mean free path forionization by collision with the molecules of the medium to providefurther secondary charged particles, and means for accelerating saidparticles into a particle beam.

6. Apparatus for creating and collectingv a charged-particle beamincluding: a radioactive source providing charged-particle emission,means disposed in a region adjacent said source that aresecondary-emission charged-particle radiation responsive to said source,said source and said responsive means being disposed -in a confinedgaseous medium. means for impressing tial source connected between saidradioactive source and said responsive electrode.

10. Apparatus for creating and controlling an electron beam including: aradioactive source providing charged-particle emission, an electrodedisposed in a region adjacent said source that is Usecondary-emissionelectron radiation responsive to said source. the said source and saidelectrode being disposed in a confined gaseous medium, a solenoidenergized from a direct current electrical y source disposed adjacentsaid radioactive source a magnetic field on said source particles tode'- e fiect said source particles against said responsive means atoblique angles and to deflect said secondary particles successivelyagainst said material to provide further secondary emission particlesand to extend the paths of said secondary particles beyond the mean freepath for ionization by collision with the molecules of the medium toprovide further secondary charged particles, means for accelerating saidparticles into a particle beam and collecting said particles.

7. Apparatus for creating and controlling an electron beam including: aradioactive source providing charged-particle emission, means disposedin a region adjacent said source that are secondary-emission electronradiation responsive to said source. said source and said responsivemeans being disposed in a confined gaseous medium. means for impressinga magnetic field on said source radiation particles to deflect saidparticles at oblique angles against said responsive means and to deflectsaid electrons successively against said responsive means to providefurther secondary electrons and to extend' the paths of said electronsbeyond the mean free path for ionization by collision with the moleculesof the medium to provide further electrons. means for accelerating saidparticles into an electron beam. and means for varying the electrostaticpotential of said source.

8. Apparatus for creating an electron beam including: a radioactivesource providing chargedparticle emission, an electrode disposed in aregion adjacent said source that is secondaryemission electron radiationresponsive'to said source, the said source and said electrode beingdisposed in a confined gaseous medium, a solenoid energized from adirect current electrical source disposed adjacent said radioactivesource and said electrode, an accelerating electrode disposed adjacentsaid responsive electrode, an electrical potential source connectedbetween said accelerating electrode and said responsive electrode, and abiasing electrical potential source connected between said acceleratingelectrode and said responsive electrode, and a biasing electricalpotential source connected between said radioactive source and saidresponsive electrode.

9. Apparatus for creating and controlling an electron beam including: aradioactive source providing charged-particle emission, an electrodedisposed in 'a region adjacent said source that is secondary-emissionelectron radiation responsive to said source, the said source and saidelectrode being disposed in a confined gaseous medium, a. solenoidenergized from a direct current lelectrical source disposed adjacentsaid radioactive source and said electrode, an accelerating electrodedisposed adjacent said responsive electrode, a collecting potentialsource connected be'- tween said 'accelerating electrode and saidresponsive electrode, and a biasing electrical potenand said electrode,an accelerating electrode disposed adjacent said responsive electrode,an electrical potential source connected between said acceleratingelectrode and said responsive electrode, a biasing electrical potentialsource, and a transformer the primary of which is connected to a sourceof alternating current and the secondary of which is connected in serieswith said biasing source between said radioactive source and saidresponsive electrode.

11. Apparatus forlcreating and controlling an electron beam including: aradioactive source providing charged-particle emission, an electrodedisposed in a region adjacent said source that is secondary-emissionelectron radiation responsive to said source, the said source and saidelectrode being disposed in a confined gaseous medium, a permanentmagnet disposed adjacent said radioactive source and said electrode, anaccelerating electrode disposed adjacent said responsive electrode, anelectrical potential source connected between said acceleratingelectrode and said responsive electrode, a biasing electrical potentialsource, and a transformer the primary of which is -connected to a sourceof alternating current and the secondary of which is connected in serieswith said biasing source between said radioactive source and saidresponsive electron.

12. Apparatus for creating and controlling an electron beam l including:an electrode and a radioactive source mountedw thereon providingcharged-particle emission, a second electrode that is Secondary emissionelectron radiation responsive to said source and disposed in a regionadjacent said source electrode, the said source electrode and saidresponsive electrode being disposed in a confined gaseous medium, asolenoid energized from a direct current electrical source disposedadjacent said radioactive source and said electrode, an accelerating andcollecting electrode disposed adjacent said responsive electrodes andsaid source, an accelerating electrical potential source, a load, atransformer and a biasing electrical potential source, acceleratingsource, the load, the secondary coil of the transformer and the biasingsource being connected in series with each other and between saidcollecting electrode and said radioactive source electrode, the primaryof said transformer being connected to a source of alternating current.

13. Apparatus for creating and controlling an electron beam including:an electrode and a radioactive source mounted thereon providingcharged-particle emission, an electrode disposed in a region adjacentsaid source that is second ary-emission electron radiation responsive tosaid source, the said source electrode and said responsive electrodebeing disposed in a confined gaseous medium, a solenoid energized from adirect current electrical source disposed adjacent said radioactivesource and said responsive electrode. an accelerating and collectingelectrode disposed adjacent said source and said responsive electrodes,an electrical potential source, a load,

a,sao,cos 9 10 and a biasing electrical potential source. the elec-REFERENCES CITED ma smn' the 10nd' and the biasing source The followingreferences are of record in the `being connected in series with eachother and me of this patent:

between said source electrode and said collecting electrode, a griddisposed between said source 5 UNITED STATES PATENTS electrode and saidresponsive electrode, and a Number Name Date transformer the primary ofwhich is connected 2,372,328 Labin Mar. 27, 1945 to a source ofalternating current and the secondary of which is connected between saidbiasing source and said grid. lo

ERNEST G. LINDER.

